1. Field of the Invention
This invention relates to an improved method for regeneration of coke-selectivated ZSM-5 type crystalline aluminosilicate zeolite catalyst by treatment with hydrogen at elevated temperature.
2. The Prior Art
It has heretofore been known to employ coke-selectivated catalysts comprising a crystalline aluminosilicate zeolite having a silica to alumina mole ratio of at least about 12 and a constraint index between about 1 and about 12 for conversion of various organic compounds involving reactions such as alkylation, disproportionation, isomerization, cracking, polymerization, aromatization, etc. These catalysts have been found to be particularly useful in selective processes, such as selective toluene disproportionation and aromatics alkylation with olefins; as disclosed in U.S. Pat. No. 4,128,592 (Kaeding). The coke-selectivated catalysts so employed slowly deactivate with time on stream ultimately making regeneration thereof necessary.
Regeneration has heretofore been carried out by contacting the aged catalyst at an elevated temperature with an oxygen-containing atmosphere, e.g., air, to effect removal of coke therefrom. Such procedure has served to restore the activity of the catalyst but has resulted in very substantial reduction in selectivity of the catalyst, approaching that of the unselectivated zeolite. Thus, after air regeneration, the catalyt has required reselectivation, i.e., controlled precoking, to restore the desired initial selectivity.